This invention relates generally to ink jet printers, and more particularly to a technique for generating printer masks that facilitate a substantially even distribution of workload among print head nozzles during the printing of repeated patterns.
It is generally known to use ink jet printers in textile printing. A relatively high proportion of printing operations in the textile printing industry include patterns that are repeatedly printed onto a substrate, e.g., fabric, paper, and the like. In printing these patterns, multi-pass printing techniques are typically implemented.
In multipass printing, a print head nozzle array is divided into a plurality of nozzle regions and different parts of the printing output are printed using different nozzle regions. The printing is done in a plurality of printing passes with the different nozzle regions firing in different passes. Also, the print substrate is advanced at fractional increments of the print head width such that, only some nozzle regions are available to print at particular pixel locations during each swath. In addition, other nozzle regions are made available in subsequent passes.
It is also generally known to use masks to control the operation of print head nozzles during printing processes. The masks control which nozzles are to be fired, the location in the pattern they are to be fired, and in which passes the nozzles are to be fired. Typically, a particular set of mask may be chosen to correspond to a predetermined print mode. Known software tools may generate these masks via a mask generator. A set of masks may be used to control the nozzles of a print head during a printing pattern, with each mask controlling a single pass. When printing a repeating pattern, the use of a single set of constant masks may result in some of the print head nozzles being fired more than others.
Printing masks may be used to control the firing of nozzles regardless of the type of ink jet printing method employed. There are two commonly used technologies by which ink droplet ejection is achieved. These technologies are thermal (or bubble-jet) ink jet printing and piezo-electric (or impulse) ink jet printing. In thermal ink jet printing, the energy for ink drop ejection is generated by resistor elements, which are electrically heated. Such elements heat rapidly in response to electrical signals controlled by a microprocessor and creates a vapor bubble that expels ink through one or more jets associated with the resistor elements. In piezo-electric ink jet printing, ink drops are ejected in response to the vibrations of a piezo-electric crystal. The piezo-electric crystal responds to an electrical signal controlled by a microprocessor.
FIG. 1A illustrates an example of the usage frequency of nozzles in a conventional generic print head after printing a first of several repeated patterns using constant print masks. The print head 100 has nozzles N1-Nn. A constant set of masks 105 controls the operation of the nozzles N1-Nn as described hereinabove. FIG. 1A also includes a histogram 110 that illustrates graphically the usage of nozzles N1-Nn. As illustrated in the histogram 110, in printing the first of several patterns, nozzles N2 and N7 were most frequently used. Also according to the histogram 110, nozzles N1 and N6 were the least frequently used. Because a constant set of masks is used for the printing of each of the repeated patterns, the frequency of usage illustrated in the histogram 110 is substantially similar. Therefore FIG. 1A is representative of nozzle usage after each pattern is printed.
FIG. 1B illustrates an example of the frequency of nozzle usage in a conventional print head 100 after printing a second of several repeating patterns using constant print masks. Again the constant set of masks 105 control the operation of the nozzles N1-Nn as discussed hereinabove. FIG. 1B also includes a histogram 120 that graphically shows the compounded effect of continued use of the same set of constant masks 105 to control the firing of the print head nozzles N1-Nn. Again, the nozzles N2 and N7 are the most frequently used and the nozzles N1 and N6 are the least frequently used. However, because the histogram 120 in FIG. 1B includes the usage after printing the first pattern in addition to the usage after printing the second pattern, the disparity between the more frequently fired nozzles N2 and N7 and the least frequently fired nozzles N1 and N6 is even greater than in FIG. 1A.
FIG. 1B also shows a failure line 130 to the right of the histogram 120. The failure line 130 represents the points at which each nozzle may fail because of over-use. As illustrated in FIG. 1B, continued printing with the constant set of masks 105 will result in the frequency of usage of the nozzles N2 and N7 approaching the failure line 130 sooner than that of the nozzles N1 and N6.
One disadvantage associated with the use of a constant set of print masks for printing repeating patterns is that some of the nozzles (the nozzles N2 and N7 for example) may be adversely stressed. For example, in thermal inkjet printers, the resistor elements associated with the adversely stressed nozzles may break down. In addition, in piezo-electric printers, the piezo-electric crystals associated with the adversely stressed nozzles may malfunction. Because overworked nozzles may malfunction, the printed patterns and the reliability of the print head may be compromised.
In addition, as stated hereinabove, the nozzles become inoperable with continued firing. When a certain percentage of the nozzles in a print head become inoperable, thereby exceeding a threshold percentage, the print head must be replaced to avoid deterioration in print quality. In printing repeating patterns with a constant set of masks, certain of the nozzles may become inoperable sooner than would be expected under nominal printing conditions. In this respect, as the rate of nozzle inoperability increases, the print heads must be replaced at a rate faster than would be expected under nominal printing conditions, thus requiring that additional print heads be used during the printing process. One result is that a user or operator must intervene to manually replace the print heads, thus reducing the overall efficiency of the printing process. Moreover, at least by virtue of the requirement of additional print heads, the overall costs in performing the printing operation may increase.
In accordance with one aspect, the invention pertains to a method for prolonging the life of a print head. The print head is used for printing a repeating pattern on a substrate. In this respect, the method includes the step of analyzing a repeating pattern. Additionally, in this respect, the method also includes the step of creating Z set(s) of print masks based on the results from the analysis of the repeating pattern.
According to another aspect, the present invention pertains to a method for printing a repeating pattern. In this respect, the method includes the steps of providing a print head with a plurality of nozzles. The method also includes the step of analyzing a repeating pattern. Based on the analysis of the repeating pattern, a set of masks that substantially balances the nozzle usage is created.
According to another aspect, the present invention pertains to a printer for printing a repeating pattern on a substrate. In this aspect the printer includes a print head with a plurality of nozzles. The printer also includes a controller for controlling print head functions including the firing of the print head nozzles. According to this aspect, the controller is configured to analyze the repeating pattern. The controller includes a mask generator operable to generate Z set(s) of masks. The masks are generated in response to the analysis of the repeating pattern.
In comparison to known prior art, certain embodiments of the invention are capable of achieving certain advantages, including some or all of the following: distributing workload more evenly among the print head nozzles; increasing print head life; improving printing efficiency; and reducing the costs associated with printing. Those skilled in the art will appreciate these and other advantages and benefits of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings.